This invention relates to emitters of mid-band infrared radiation having a wavelength in the range of 2-5 microns and, more particularly, to an emitter constructed as a semiconductor laser.
Jamming of an infrared heat seeking missile, for the purpose of protecting a friendly aircraft, has been accomplished by transmitting a beam of infrared radiation wherein the radiation amplitude is modulated in the manner of a train of pulses. Such a beam of amplitude modulated, or chopped, radiation is directed at the missile. As is well known, such missiles have a detector assembly which responds to incident radiation to produce a detected signal. The missiles are operative to detect a direction of incident radiation of substantially constant amplitude by a process of chopping the detected signal to gain phase data which directs the missile in the azimuthal and the elevation coordinates for tracking a source of the radiation. The presence of a jamming chopped infrared signal introduces additional pulses to the missile's detected signal resulting in the development of directional errors which drive the missile off course.
A problem exists in that infrared emitters of presently available countermeasures equipment are unduly large and heavy resulting in a diminution of the flight capabilities of aircraft carrying such equipment. By way of example, one such emitter is a cesium arc lamp. Due to the relatively low intensity of the emitted radiation, the emitter has a large reflector to gather and to collimate the radiation to provide a beam of adequate intensity to jam the missile. The transmitter with its electronic modulation equipment add significant weight to the aircraft. Another example of an emitter employs an incandescent heat source which is unduly large and expensive. In the case of the foregoing reflector, such a reflector may have to be mounted partially or completely outside of the aircraft skin. This introduces excessive drag, particularly at high aircraft speed. Furthermore, existing countermeasure emitters may not provide sufficient power to jam a missile at long range from the aircraft carrying such an emitter.